This invention relates to a clutch of the type in which a helical spring is telescoped over rotatably mounted input and output hubs.
Such a clutch is disclosed in MacDonald U.S. Pat. No. 3,915,268. In that clutch, the spring tends to naturally wrap down into gripping engagement with both hubs to couple the output hub for rotation with the input hub. The spring is formed with a radially extending tang which is acted upon by an axially movable actuator. When the actuator is moved axially to a clutch-disengaging position, it causes the tang to turn in a direction to unwrap the spring from the input hub and thereby allow the input hub to rotate relative to the output hub. When the actuator is shifted reversely to a clutch-engaging position, the inherent resiliency of the spring causes the tang to turn in the opposite direction and causes the spring to wrap down upon the input hub and to couple the input hub to the output hub.
The clutch disclosed in the MacDonald patent is of the so-called deadman type in that the actuator normally is held in a position to effect disengagement of the clutch. The clutch can be engaged only by manually shifting the actuator and, if the actuator is manually released, the clutch automatically disengages.